Add a security scanner api config object for params

Change SecScanAPI to use a uri creation func instead of test context

Pass config provider through validator context

Remove app config dependency for validators

util/__init__.py

@@ -1,3 +1,6 @@
+from flask import url_for
+from urlparse import urljoin
+
 def get_app_url(config):
   """ Returns the application's URL, based on the given config. """
   return '%s://%s' % (config['PREFERRED_URL_SCHEME'], config['SERVER_HOSTNAME'])
@@ -19,3 +22,13 @@ def slash_join(*args):
 
   args = [rmslash(path) for path in args]
   return '/'.join(args)
+
+def create_uri_func_from_context(context, url_scheme_and_hostname):
+  def create_uri(repository_and_namespace, checksum):
+    with context:
+      relative_layer_url = url_for('v2.download_blob', repository=repository_and_namespace,
+                                   digest=checksum)
+    return urljoin(get_app_url_from_scheme_hostname(url_scheme_and_hostname), relative_layer_url)
+
+  return create_uri
+